Capacity and reads can be monitored by using the zpool
iostat command.

Single or multiple cache devices can be added when the pool
is created. They can also be added and removed after the pool is created.
For more information, see Example 4–4.

Cache devices cannot be mirrored or be part of a RAID-Z configuration.

If a read error is encountered on a cache device, that read
I/O is reissued to the original storage pool device, which might be part of
a mirrored or a RAID-Z configuration. The content of the cache devices is
considered volatile, similar to other system caches.